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The interest to assess the relationship between forest gap characteristics and topography features has been growing in the last decades. However, such an approach has not been studied in undisturbed mixed sessile oak–beech old-growth forests. Therefore, the present study carried out in one of the best-preserved sessile oak–beech old-growth forests in Europe, aims to assess the influence of topographic features (slope, altitude and aspect) on (i) some characteristics of canopies and expanded gaps (surface, diameter and perimeter) and (ii) the proportion of beech and sessile oak as bordering trees, gap fillers and gap makers. Through a complete gap survey on an area of 32 ha, 321 gaps were identified and mapped. The largest gaps and also the highest gap frequency (140) was found in the slope class (15.1–20°), while the gap frequency increased with altitude, with 99 gaps being recorded at 601–650 m a.s.l. The size and perimeter of the canopy and expanded gaps, as well as the number of gap makers, were negatively related to the slope and altitude. The expanded gap to canopy gap size ratio decreased with the slope and was positively related to the altitude, while a significant negative decrease in gap filler density with altitude was encountered. The sessile oak participation ratio as bordering trees forming the gap increased not only with the altitude but also with the slope. The topography plays an important role in the formation of gaps as well as in the characteristics of the future stand. This study provides valuable insights into the relationship between canopy gap characteristics and topography, which is useful information for forest owners that pursue the design of forest management toward nature-based solutions.

Deadwood is a fundamental structural and functional component of forests, with a crucial role in supporting forest biodiversity, nutrient and carbon cycling. Precise deadwood density estimates and its relation to envi-ronmental factors are necessary to evaluate the biomass and carbon stocked in this component. In this study, we estimated dry deadwood density for two different tree species, silver fir (Abies alba) and European beech (Fagus sylvatica) and for three snags and five logs decomposition classes in a virgin mixed beech-fir forest in the Southern Carpathians. The goal was to assess how deadwood density is influenced by different abiotic (moisture, elevation, slope, aspect) and wood-related factors (rottenness, position along the piece, contact with the soil). For snags, the mean dry density showed a reduced variability within decomposition classes (484-326 kg.m- 3 for beech and 374-319 kg.m- 3 for fir), compared to the logs (486-139 kg.m- 3 for beech and 359-161 kg.m- 3 for fir). While the mass moisture varied slowly in the first three decay classes (around 60-80 %), it increased sharply in the last two decay classes of logs (>140 % in the fourth class and > 350 % in the last one). The rottenness increased with the decay class in a similar way for both species. The contact of logs with the soil influenced positively the moisture, but the position of the sampling within the piece did not play any significant role in the variability of density. Based on density estimates per decay classes we estimated that the carbon (C) stored in deadwood varied greatly among the 21 plots from 0.36 to 41.16 MgC ha-1, with a mean value of 15.96 +/- 2.36 (+/- SE) MgC ha-1. Our study suggests that volume-based calculations might yield biased quantitative estimates of C stored in deadwood unless a local estimate of dead wood density corrected per species and decomposition class is applied. Moreover, the use of an averaged value of dry density instead of value for each decay class may result in an overestimation of 22% on the estimation of C stock. Thus, our study emphasises the importance of considering decay class-specific values in future inventories of C stocks in other forests and for other species. Furthermore, it could serve as a methodological basis for more specific research designed to uncover the potential influence of different forest management practices on dry deadwood density.

Key message Climate-warming related replacement of beech by oak forests in the course of natural forest succession or silvicultural decisions may considerably reduce ecosystem carbon storage of central European woodlands. Context Climate warming may change the carbon (C) storage in forest biomass and soil through future shifts in tree species composition. With a projected warming by 2–3 K over the twenty-first century, silvicultural adaptation measures and natural succession might lead to the replacement of European beech forests by thermophilic oak forests in drought- and heat-affected regions of central and south-eastern Europe, but the consequences for ecosystem C storage of this species shift are not clear. Aims To quantify the change in C storage in biomass and soil with a shift from beech (Fagus sylvatica) to oak forest (Quercus petraea, Q. frainetto, Q. cerris), we measured the aboveground biomass (AGC) and soil C pools (SOC). Methods AGC pools and SOC stocks to − 100 cm depth were calculated from forest inventory and volume-related SOC content data for beech, mixed beech-oak and oak forests in three transects in the natural beech-oak ecotone of western Romania, where beech occurs at its heat- and drought-induced distribution limit. Results From the cooler, more humid beech forests to the warmer, more xeric oak forests, which are 1–2 K warmer, AGC and SOC pools decreased by about 22% (40 Mg C ha−1) and 20% (17 Mg C ha−1), respectively. The likely main drivers are indirect temperature effects acting through tree species and management in the case of AGC, but direct temperature effects for SOC. Conclusion If drought- and heat-affected beech forests in Central Europe are replaced by thermophilic oak forests in future, this will lead to carbon losses of ~ 50–60 Mg ha−1, thus reducing ecosystem carbon storage substantially.

Studying spatial patterns and habitat association of plant communities may provide understanding of the ecological mechanisms and processes that maintain species coexistence. To conduct assessments of correlation between community compositions and habitat association, we used data from two topographically different plots with 2 ha area in tropical evergreen forests with the variables recorded via grid systems of 10 × 10 m subplots in Northern-Central Vietnam. First, we tested the relationship between community composition and species diversity indices considering the topographical variables. We then assessed the interspecific interactions of 20 dominant plant species using the nearest-neighbor distribution function, Dij(r), and Ripley’s K-function, Kij(r). Based on the significant spatial association of species pairs, indices of interspecific interaction were calculated by the quantitative amounts of the summary statistics. The results showed that (i) community compositions were significantly influenced by the topographic variables and (ii) almost 50% significant pairs of species interactions were increased with increasing spatial scales up to 10–15 m, then declined and disappeared at scales of 30–40 m. Segregation and partial overlap were the dominant association types and disappeared at larger spatial scales. Spatial segregation, mixing, and partial overlap revealed the important species interactions in maintaining species coexistence under habitat heterogeneity in diverse forest communities.

International audience; Just as the aboveground tree organs represent the interface between trees and the atmosphere, roots act as the interface between trees and the soil. In this function, roots take-up water and nutrients, facilitate interactions with soil microflora, anchor trees, and also contribute to the gross primary production of forests. However, in comparison to aboveground plant organs, the biomass of roots is much more difficult to study. In this study, we analyzed 19 European datasets on above- and belowground biomass of juvenile trees of 14 species to identify generalizable estimators of root biomass based on tree sapling dimensions (e.g. height, diameter, aboveground biomass). Such estimations are essential growth and sequestration modelling. In addition, the intention was to study the effect of sapling dimension and light availability on biomass allocation to roots. All aboveground variables were significant predictors for root biomass. But, among aboveground predictors of root biomass plant height performed poorest. When comparing conifer and broadleaf species, the latter tended to have a higher root biomass at a given dimension. Also, with increasing size, the share of belowground biomass tended to increase for the sapling dimensions considered. In most species, there was a trend of increasing relative belowground biomass with increasing light availability. Finally, the height to diameter ratio (H/D) was negatively correlated to relative belowground biomass. This indicates that trees with a high H/D are not only more unstable owing to the unfavorable bending stress resistance, but also because they are comparatively less well anchored in the ground. Thus, single tree stability may be improved through increasing light availability to increase the share of belowground biomass.

Worldwide increases in droughts- and heat-waves-associated tree mortality events are destabilizing the future of many forests and the ecosystem services they provide. Along with climate, understanding the impact of the legacies of past forest management is key to better explain current responses of different tree species to climate change. We studied tree mortality events that peaked in 2012 affecting one native (silver fir; growing within its natural distribution range) and two introduced (black pine and Scots; growing outside their natural distribution range) conifer species from the Romanian Carpathians. The three conifers were compared in terms of mortality events, growth trends, growth resilience to severe drought events, climate-growth relationships, and regeneration patterns. The mortality rates of the three species were found to be associated with severe drought events. Nevertheless, the native silver fir seems to undergo a self-thinning process, while the future of the remaining living black pine and Scots pine trees is uncertain as they register significant negative growth trends. Overall, the native silver fir showed a higher resilience to severe drought events than the two introduced pine species. Furthermore, and unlike the native silver fir, black pine and Scots pine species do not successfully regenerate. A high diversity of native broadleaf species sprouts and develops instead under them suggesting that we might be witnessing a process of ecological succession, with broadleaves recovering their habitats. As native species seem to perform better in terms of resilience and regeneration than introduced species, the overall effect of the black pine and Scots pine mortality might be compensated. Legacies of past forest management should be taken into account in order to better understand current responses of different tree species to ongoing climate change.

The diversity relationship between tree and herb layer has often been investigated, but the results are contradictory. Moreover, few studies of deciduous European species have been conducted to date in natural or near-natural forests, while such studies in old-growth forest with considerable co-dominance of oak are missing. In one of the best preserved natural European beech-sessile oak forests (Runcu-Grosi Natural Reserve, Western Romania) we investigated whether there is a correlation between canopy-layer diversity and herb-layer diversity. Structural diversity, vegetation composition, ecological and functional traits were evaluated. Our results show that the herb-layer diversity is higher under canopy with greater tree-layer diversity, and the diversity of both layers depend on whether the overstorey is dominated by beech or sessile oak. Herb layers of plots with oak co-dominance showed higher indicator values for light and temperature, and a higher proportion of graminoides and shrub species. In contrast, herb-layer in beech plots is dominated by juvenile trees, mainly beech and competitive herb species. Oak plots are characterised by a generally more evenly distributed herb-layer composition. Species richness of herb-layer was higher under a diversely structured overstorey, which was mainly achieved when oak was present in the canopy, and correlated negatively with litter thickness, which was highest in beech plots. We conclude that the identity of the dominant canopy species is most important for herb layer species composition and diversity. Furthermore, the plots with oak occurrence in the overstorey even with weak proportion (around 20% of stand basal area) features a higher biodiversity of species in the understorey.

In a changing climate, forest managers need to select productive and climate-change-resilient tree species and provenances. Therefore, assessing the growth response of provenances growing in field trials to climate provides useful information for identifying the more appropriate provenance or variety. To determine the genetic gain through selection of the most productive and resilient families and to decipher the role of crown forms of Norway spruces (Picea abies (L.) Karst.), we used 24 families with a classical crown (pyramidalis) and 24 with a narrow crown (pendula) from eight provenances, growing in a 25-year-old comparative trial. The annual wood characteristics (ring width and early- and latewood), the wood resistance (expressed by latewood proportion (LWP)), and the growth response to climate of the two spruce crown forms were investigated. No significant differences between the two spruce forms were found regarding the ring width characteristics. However, three pendula families of Stâna de Vale I provenance exhibited the highest LWP and could be included in a future selection strategy, the respective trait having also high heritability. Radial growth was positively and significantly correlated with previous September and current July precipitation and negatively with current June temperature. Both spruce forms showed good recovery capacity after a drought event.

Climate warming-related drought could become a major driver of large-scale forest dieback. However, little is known about how past management legacies modulate the climate-growth responses during recent dieback episodes in central European oak forests. Here, we examine the role played by past management –unmanaged old-growth vs. managed forests– in recent tree mortality events occurring in Quercus petraea (Matt.) Liebl. stands across large areas of western Romania. We analyze how stand structure (tree size, competition) and climatic factors (drought, temperature and precipitation) drive tree radial growth patterns in neighboring standing dead and living trees. We analyzed basal area increments (BAI) trends, past management legacies and climate- and drought-growth relationships during the 20th century to distinguish the roles and interactions on recent warming-induced dieback. We observed that temperature rises and changes in atmospheric water demand during growing season let to increasing drought stress during the late 20th century affecting both managed and unmanaged forests. Dead trees from old-growth and managed forests showed lower growth than living trees after dieback onset. In both forests, dead and living trees displayed divergent growth patterns after dry 1980s, indicating that dieback was triggered by severe extreme conditions. Dead trees from managed stands experienced significant stronger growth reductions after 1980s though they experienced less tree-to-tree competition than dead trees in old-growth forest. High stand density negatively drove growth and enhanced climate sensitivity in old-growth stands. Competition acted synergistically with climate warming and drought causing tree mortality regardless of the management legacies in of Q. petraea forests. Our retrospective assessment of growth rates in relation with climate and structure changes offers valuable information for further forest conservation and management decisions of Q. petraea forests. These findings highlight the importance of past uses legacies driving recent forest dieback in temperate oak forests, making them more vulnerable under forecasted climate-warming related droughts in central Europe., This work was supported by NEMKLIM project: Nemoral Forests under Climate Extremes (NEMKLIM Project, grant number 3517861300), financed by the German Federal Agency for Nature Conservation (Bundesamt für Naturschutz,BfN) and the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, Germany and by project PN 19070506 financed by Romanian National Authority from Scientific Research and Innovation. I.C. Petritan was supported by a grant of the Romanian Ministry of Education and Research, CNCS-UEFISCDI, project number PN-III-P4-ID-PCE-2020- 2696, within PNCDI III. R. S ´anchez-Salguero was supported by VUL-BOS project (UPO-1263216, FEDER Funds, Andalusia Regional Government, Consejería de Economía, Conocimiento, Empresas y Universidad 2014-2020) and LESENS (RTI2018-096884-B-C33) project from the Spanish Ministry of Science, Innovation and Universities. A. Hevia was supported by PinCaR project (UHU-1266324, FEDER Funds, Andalusia Regional Government, Consejería de Economía, Conocimiento, Empresas y Universidad 2014-2020). We are also grateful to Lucian Toiu, Nicu Tudose, George Sarbu and Gheorghe Stefan for help in collecting field data. We appreciate the permission and logistic support given by staff of the Barzava and Codrii Beiusului si Sfanta Maria Forest Districts, we are grateful especially to eng. Gheorghe Marc and eng. Jeno Ferko. The authors declare no conflicts of interest.Nemoral Forests under Climate Extremes (NEMKLIM Project, grant number 3517861300), German Federal Agency for Nature Conservation (Bundesamt für Naturschutz,BfN), German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, Germany, project PN 19070506, Romanian National Authority from Scientific Research and Innovation, Romanian Ministry of Education and Research, CNCS-UEFISCDI, project number PN-III-P4-ID-PCE-2020- 2696, within PNCDI III. projects VUL-BOS project (UPO-1263216 and PinCaR (UHU-1266324), FEDER Funds, Andalusia Regional Government, Consejería de Economía, Conocimiento, Empresas y Universidad 2014-2020), project LESENS (RTI2018-096884-B-C33), Spanish Ministry of Science, Innovation and Universities.

Deadwood is a fundamental forest habitat component and highly important for biodiversity conservation. Its availability, composition, size, categories and distribution depend on various structural and environmental factors (e.g., forest age, management, tree mortality, climate, decomposition). We analysed deadwood patterns along altitudinal gradients of managed (three) and unmanaged (one) deciduous forests in Western Romania. A total of 153 plots (119 managed, 34 unmanaged) of four pre-classified forest types dominated by Fagus sylvatica, Quercus petraea, Quercus frainetto with Quercus cerris, and Tilia tomentosa were evaluated, the former two both in managed and unmanaged stands. The managed forest types displayed an average deadwood volume of 47 m3 ha−1 with lying deadwood accounting for over 70%. About 40% of deadwood objects occurred in the early to intermediate decomposition stage. Deadwood volumes in unmanaged forest types exceeded those of managed forests two- to threefold although the deadwood amounts observed in managed forests were similar to low-intervention or recently abandoned forests, lying within critical threshold values considered important for the long-term preservation of biodiversity. Linear-mixed-effects models confirmed the positive impact of non-management and the negative effect of annual mean temperature on deadwood volume. Prediction models suggested that management and annual mean temperature showed additive effects, indicating that a combination of environmental and structural parameters determines the amount of deadwood in the studied forest types. As climatic variables strongly influence tree species composition and thus forest type, management involving deadwood retention or accumulation should consider forest-type specific characteristics and thresholds.

Old-growth forests are often looked at as reference for close to nature silviculture, which aims to manage forests in a natural way. An important component of these forests is the large amount of deadwood they possess; the role of dead wood in the forest ecosystem has been well recognised. A detailed investigation of dead wood characteristics (the amount per stand, species, dead wood type, decay class, size and spatial distribution) was performed in two Romanian old-growth European mixed beech forests: Runcu Grosi Reserve (sessile oak-beech) and Sinca (silver fir-beech). Dead wood pieces were classified as belonging to one of seven dead wood types and one of five decay classes. The total amount of the dead wood was greater in Runcu Grosi (240.8 m3 ha-1) than in Sinca Forest (135.5 m3 ha-1). The majority of the dead wood in Runcu Grosi was composed of sessile oak (91.7%), whereas in Sinca Forest, the main dead wood species was silver fir (67.0%); both species exhibited higher values of probability density than beech, the second most important species. The dead wood exhibited much variation in tree size and in dead wood type, and covered the entire spectrum of decomposition classes. The main spatial pattern of all standing dead trees was random in both forests (over 55%), with a reduced participation of regularity and aggregation. The results of this investigation could be used as key values derived from natural conditions to enhance the biodiversity related to dead wood in managed temperate beech mixed forests.

Light availability in forests is a strong driver for forest development and diversity. Tree species develop differently under varying levels of light. Understanding the reasons for the individual growth strategies of tree species is crucial to understand dynamics of forest communities. This study aims at further disentangling aboveground biomass allocation patterns and growth variables for saplings of the tree species sycamore maple (Acer pseudoplatanus L.), European beech (Fagus sylvatica L.), and European ash (Fraxinus excelsior L.). Plants were destructively sampled along a light gradient. European beech allocated more biomass to its branches and less to its stem, in comparison to the other two species. The relative growth rate (RGR) and leaf mass area (LMA) of all species increased towards an asymptote along the increasing light gradient, whereas the leaf are ratio (LAR) decreased. The rate of increase and decrease differed among the tree species. Net assimilation rate (NAR) and absolute growth rate (AGR) both also increased with light availability, but the distinction among the species was not as clear. This study showed varying reactions of all three species to light and allowed a quantitative distinction among the species regarding their shade tolerance (ash

In this study, different approaches were used to investigate the vulnerability of beech forests, located at the eastern limit of their natural range, to climate change. To accomplish this, six 2500 m2 plots were sampled in four European beech forest genetic resources, located in Romania at different altitudinal levels, varying from 230 to 580 m in the Bacău hills and between 650 and 1300 m in the Curvature Carpathian (Braşov region). The analysis of trees phenotypic traits, their radial growth, and the regeneration, did not indicate a vulnerability of the sampled stands to the fluctuations of the environmental factors from the 1950-2014 period. The growth indices of all three populations of Bacău hills are negatively correlated with both June air temperature of current year and September of the previous year. The precipitation amount of September previous year positively influenced the growth indices. The radial growth of plots in Braşov region is slightly linked to the climate. The temperature during the growing season represents a limiting factor for stands that are located outside of the optimal altitudinal species distribution (600-1200 m, in Romania), especially at low altitudes. Our results indicated that a rise of the temperature accompanied by a possible reduction of the precipitations (as is predicted for the coming years) could increase the sensibility of beech forests at lower altitude.

Climate change-induced tree mortality is occurring worldwide, at increasingly larger scales and with increasing frequency. How climate change-induced tree mortality could affect the ecology and carbon (C) sink capacity of soils remains unknown. This study investigated regional-scale drought-induced tree mortality, based on events that occurred after a very dry year (2012) in the Carpathians mountain range (Romania), which caused mortality in three common conifer species: Scots pine, Black pine, and Silver fir. This resulted in hot-spots of biogenic soil CO 2 emissions (soil respiration; Rs). Four to five years after the main mortality event, Rs-related soil CO 2 emissions under dead trees were, on average, 21% (ranging from 18 to 35%) higher than CO 2 emissions under living trees. Total (Rs) and heterotrophic (R H )-related soil CO 2 emissions were strongly related to alterations in the soil environment following tree mortality (e.g. changes in quantity and quality of soil organic matter, microclimate, pH or fine root demography). Moreover, the massive mortality event of 2012 resulted in greater presence of successional vegetation (broadleaf seedlings, shrubland and grasses), which may control the environmental factors that either directly or indirectly affected biotic soil fluxes (Rs and R H ). Besides the well-known direct effects of climate change on soil CO 2 emissions, the cascading effects triggered by climate change-induced tree mortality could also exert a strong indirect impact on soil CO 2 emissions. Overall, climate change-induced tree mortality alters the magnitude of environmental controls on Rs and hence determines how the ecosystem C budget responds to climate change. © 2019 Elsevier Ltd This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) with the projects VERONICA ( CGL2013-42271-P ) and the project IBERYCA ( CGL2017-84723-P ), and by the Romanian Ministry of Education and Scientific Research through UEFISCDI with the projects TREEMORIS ( PN-II-RU-TE-2014-4-0791 ), NATIvE ( PN-III-P1-1.1-PD-2016-0583 ), and BIOCARB ( PN-III-P1-1.1-TE-2016-1508 ). This research was also supported by the Basque Government through the BERC 2018-2021 program, and by the Spanish Ministry of Economy and Competitiveness (MINECO) through the BC3 María de Maeztu excellence accreditation ( MDM-2017-0714 ). I.C. Petritan was partially funded by the H2020/ERA-NET/ERA-GAS (Project 82/2017, Mobilizing and monitoring climate positive efforts in forests and forestry, FORCLIMIT ). Many thanks to Cosmin Zgremtia, Ionela Medrea, Andrei Apafaian, Raluca Enescu and Marta Ramos for their valuable help during field campaigns and laboratory work.

Ring-width series are important for diverse fields of research such as the study of past climate, forest ecology, forest genetics, and the determination of origin (dendro-provenancing) or dating of archaeological objects. Recent research suggests diverging climate-growth relationships in tree-rings due to the cardinal direction of extracting the tree cores (i.e. direction-specific effect). This presents an understudied source of bias that potentially affects many data sets in tree-ring research. In this study, we investigated possible direction-specific growth variability based on an international (10 countries), multi-species (8 species) tree-ring width network encompassing 22 sites. To estimate the effect of direction-specific growth variability on climate-growth relationships, we applied a combination of three methods: An analysis of signal strength differences, a Principal Component Gradient Analysis and a test on the direction-specific differences in correlations between indexed ring-widths series and climate variables. We found no evidence for systematic direction-specific effects on tree radial growth variability in high-pass filtered ring-width series. In addition, direction-specific growth showed only marginal effects on climate-growth correlations. These findings therefore indicate that there is no consistent bias caused by coring direction in data sets used for diverse dendrochronological applications on relatively mesic sites within forests in flat terrain, as were studied here. However, in extremely dry, warm or cold environments, or on steep slopes, and for different life-forms such as shrubs, further research is advisable., Swiss National Science Foundation, grant no. P0ZHP1_162299. A. Buras received funding from the German Academic Exchange Service (DAAD). CGL2015-69186-C2-1-R project (Spanish Ministry of Economy). DAAD-Conacyt scholarship. OLDPINE (AGL2017-83828-C2-2R) project (Spanish Ministry of Economy, Industry and Competitiveness, MINECO). Ministry of Education, Youth, and Sports of CR within the National Sustainability Program I (NPUI), grant number LO1415, the Czech Science Foundation (18-17295S). Ministry of Research and Innovation, CNCS – UEFISCDI, project number PN-III-P1-1.1-TE-2016-1508, within PNCDI III (BIOCARB). CoMo-ReAdapt (CGL2013-48843-C2-1-R, Spanish Ministry of Economy, Industry and Competitiveness, Spain), LESENS (RTI2018-096884-B-C33, Ministry of Science, Innovation and Universities, Spain).

The structural patterns and dynamics of a primeval silver fir ( Abies alba ) – European beech ( Fagus sylvatica ) forest in the Southern Carpathians (Romania) were assessed to gain deeper insight into species interactions and mechanisms of coexistence, and to study the influence of species composition on forest structure. At 21 sample plots, each covering 0.123 ha within an area of 240 ha, all living and dead trees ⩾6 cm dbh (diameter at breast height) were mapped and measured. Regeneration was assessed on four sub-plots per plot. Additionally, a 1-ha permanent plot established in 2003 was re-measured in 2013 to obtain information on stand dynamics. Point pattern analyses were conducted to study the spatial patterns and tree-to-tree interactions. The overall dbh distributions of beech and fir tended to indicate sustainable population structures. The share of beech varying from 24.8% to 95% (average 58%) in stand basal area did not influence stand parameters such as basal area or volume, nor the distribution of growing stock to different canopy layers. We found fir to dominate the lowest dbh classes in plots that were strongly dominated by beech in the top layer and vice versa, locally indicating species alternation. The regeneration density of fir was lower than of beech, although browsing by ungulates was negligible. In contrast to its share among living trees, fir contributed two-thirds to the deadwood volume. The 10-year changes in forest structure and mortality rate on the 1-ha plot were very small, suggesting the absence of recent intermediate or severe disturbances. The spatial patterns of the dead trees and of the living beech and fir in different canopy layers agreed with a disturbance regime dominated by stochastic small-scale events. Although the spatial patterns of beech and fir were similar, the tree-to-tree interactions indicated a higher intraspecific competition of beech than of fir and a higher shade tolerance of fir particularly in later stages of development. Both could be important factors for the coexistence of the two species. We conclude that the primeval fir–beech forest Sinca shows under the present small scale disturbance regime a high stability and structural resilience. Temporal changes in species composition only lead to small fluctuations in stand parameters and do not threaten the long-term coexistence of beech and fir. Forest managers may vary the species composition of fir–beech forests without substantially influencing the overall forest structure or productivity.

The European Dendroecologial Fieldweek (EDF) provides an intensive learning experience in tree-ring research that challenges any participant to explore new multidisciplinary dendro-sciences approaches within the context of field and laboratory settings. Here we present the 25th EDF, held in Asturias, NW Spain, in summer 2014. The course, with 33 participants and 10 instructors from 18 countries included advanced training in dendrochronology skills, an overview of tree-ring broad fields and methodological basics to deal with specific research questions as well as applied advanced micro-projects in dendroarchaeology (DAR), dendroclimatology (DCL), dendrogeomorphology (DGM), forest dynamic (FD) and plant anatomy (PA). The results demonstrated the potential of tree-ring research in the Asturias region. The DAR group researched archaeological samples from different contexts (Oviedo cathedral choir stalls, Segovia cathedral roof timbers, Ribadeo shipwreck ship timbers and Bronze Age site charcoal) and explored the supply of wood in different periods. The DCL group established that the Quercus robur and Castanea sativa ring-width measurements show weak climate-growth correlations, where for many trees this is likely caused by management. The strength of the climatic signal could be enhanced using undisturbed settings. The DGM group found that Corylus avellana and Salix spp. are challenging species for dendrogeomorphological studies. Debris-flow events were detected by the presence of tension wood, growth reduction and scars, and their incidences were also supported by local meteorological data. The FD group found that tree growth decreases with increasing competition, a pattern more pronounced in C. sativa than in Pinus sylvestris forest plantations. The results indicate that wood production could be increased by applying thinning treatments on C. sativa. The PA group showed that xylem conduits and phloem area are organized according to the common needs for water supply to leaves and obtain photosynthetic products, regardless site growing conditions for P. sylvestris and Tusilago farfara. In conclusion, this EDF has been a model for interdisciplinary research and international collaboration that has demonstrated that high-quality research and education can be conducted within one week. The EDFs provide an important service to the dendrochronological community and demonstrate the usefulness of this educational-scientific and multi-cultural experience.

In recent decades, natural forest remnants have become increasingly important as reference objects for maintaining or restoring old-growth characteristics in managed forests. Canopy gaps play an important role in forest regeneration, particularly for the establishment and development of tree species with different ecological recruitment patterns. Yet quantitative descriptions of such patterns are still scarce, particularly for oak-dominated forests. The old-growth sessile oak–European beech forest remnant in the Runcu-Grosi Natural Reserve provided a unique opportunity to study natural disturbance regimes with minimal human influence in an ecosystem type rarely investigated. The study site comprised the best preserved part of the Reserve. Its 32.3 ha are dominated by sessile oak. A complete gap survey was carried out. The size, shape, spatial pattern and traits of the gapmakers of all 321 gaps were recorded. Additionally, the gap age as well as the structure and composition of gapfillers were investigated in 70 randomly sampled expanded gaps. The canopy gaps and the expanded gaps covered 12.8% and 28.5% of the study site, respectively. The frequency distribution of the canopy gap sizes corresponded to the negative exponential distribution, with most of the gaps (60%) smaller than 100 m2, 34% between 100 and 300 m2 and only 2% larger than 500 m2. Canopy gaps smaller than 300 m2 were responsible for 71% of the total gap area, suggesting a dominance of small and intermediate gaps in this forest. The pattern of the canopy gaps is characterized by a pronounced soft-core effect, and in one part of the study area a tendency towards regularity. Most of the gaps (84%) were caused by more than one gapmaker and seemed to be created in more than one disturbance event since, in 72% of the gaps, gapmakers of at least two different decay classes were found. The disturbance regime was driven by the mortality of sessile oaks, the main gapmaker species, caused mostly by uprooting. The other main canopy tree species was European beech, which died often by snapping. It was less common as gapmaker (20%), but was the main gapfiller (91%). In contrast sessile oak was almost absent among the gapfillers. These results suggest that the current small-scale disturbance pattern dominating this old-growth forest is more suitable for shade–tolerant species such as European beech, accentuating the already steady decline of oaks in mixed sessile oak–European beech stands.

Tree mortality is a key factor influencing forest functions and dynamics, but our understanding of the mechanisms leading to mortality and the associated changes in tree growth rates are still limited. We compiled a new pan-continental tree-ring width database from sites where both dead and living trees were sampled (2970 dead and 4224 living trees from 190 sites, including 36 species), and compared early and recent growth rates between trees that died and those that survived a given mortality event. We observed a decrease in radial growth before death in ca. 84% of the mortality events. The extent and duration of these reductions were highly variable (1–100 years in 96% of events) due to the complex interactions among study species and the source(s) of mortality. Strong and long-lasting declines were found for gymnosperms, shade- and drought-tolerant species, and trees that died from competition. Angiosperms and trees that died due to biotic attacks (especially bark-beetles) typically showed relatively small and short-term growth reductions. Our analysis did not highlight any universal trade-off between early growth and tree longevity within a species, although this result may also reflect high variability in sampling design among sites. The intersite and interspecific variability in growth patterns before mortality provides valuable information on the nature of the mortality process, which is consistent with our understanding of the physiological mechanisms leading to mortality. Abrupt changes in growth immediately before death can be associated with generalized hydraulic failure and/or bark-beetle attack, while long-term decrease in growth may be associated with a gradual decline in hydraulic performance coupled with depletion in carbon reserves. Our results imply that growth-based mortality algorithms may be a powerful tool for predicting gymnosperm mortality induced by chronic stress, but not necessarily so for angiosperms and in case of intense drought or bark-beetle outbreaks., GGI by the Spanish Ministry of Economy and Competitiveness (Project AGL2014-61175-JIN)., AMH by the Spanish Ministry of Science and Innovation (Projects CGL2007-60120 and CSD2008-0040) and by the Spanish Ministry of Education via a FPU Scholarship., JJC, JCLC, and GSB by the Spanish Ministry of Economy (Projects CGL2015-69186-C2-1-R, CGL2013-48843-C2-2-R, and CGL2012-32965) and the EU (Project FEDER 0087 TRANSHABITAT).

The paper details an investigation of the stand structure and patterns of diversity observed in the Runcu-Grosi Natural Reserve (western Romania), one of the best preserved natural mixed sessile oak forests in Europe. The effect of the proportion of sessile oak in the stand composition on specific patterns was also studied. Comparable with other natural forests, the stands of Runcu-Grosi are characterised by a high volume (mean living tree volume of 577 m3 ha−1 in the sessile oak dominated plots and 675 in the pure beech plots), a highly differentiated diameter distribution and a large quantity of dead wood, especially in the mixed plots (approx. 135 m3 ha−1, compared to 75 in the pure beech plots). The higher volume of coarse woody debris in the mixed plots is due to the higher proportion of dead sessile oak in the reserve, which accounted for about 70% of the total dead wood in both the sessile oak and the beech dominated plots. The over proportional representation of dead sessile oak, and a very low number of oak saplings taller than 1.3 m, indicated a declining tendency of sessile oak in the stand in future. The sessile oak dominated stands exhibited a higher level of tree species diversity than those dominated by beech. Where beech was the dominant species, a high percentage of the sessile oak was present in pure groups (36%), whereas in the oak dominated stands, most of the sessile oaks were surrounded either by shade tolerant beech or by other species (ca. 75%), and were classed as either dominant or codominant trees. These species-specific patterns correspond with the silviculture of mixed oak-beech forests: without interventions to favour oak, the dominance of beech will increase.

Summary We compared shade tolerance of maple, ash and beech in the sapling stage from two sites with rich soils differing in water supply, growing in dense thickets underneath a beech shelterwood of varying canopy densities. Shade tolerance was described by two components: mortality in shade and height growth in high light. At low light, beech showed the least mortality, maple the highest and ash in between on both sites. The decline with increasing light was steepest in beech and more gradual with ash and maple. At ~ 15 per cent above canopy light, all three species approached zero mortality. Beech as the most shade-tolerant species had the highest survival rate under low light and the least length growth rate under high light (>17 per cent). Ash had a lower survival rate at low light than beech and a highest growth rate at high light. Maple showed a bit weaker trade-off with the lowest survival rate but a growth rate inferior to ash. On the better water-supplied site, height growth was signifi cantly superior in all three species only under high light. On the basis of these results, silvicultural conclusions are drawn with respect to appropriate light levels and cutting types.

Old-growth forests are often looked at as a reference for naturalness. Analyzing their successional pathways can provide valuable information on the main drivers of succession in the absence of anthropogenic influence. This knowledge could then prove particularly useful for the maintenance of mixed species stands as a management option to counteract potential changes in forest functions under foreseen climate scenarios. The study was conducted in an old growth Quercus petraea – Fagus sylvatica forest in the Runcu Grosi Natural Reserve, western Romania. Main goals of the research were to assess the structure of the old growth forest and understand how the spatial pattern of the two species is shaped by their competitive relationship. We wanted to figure out if the spatial relationship between Q. petraea and F. sylvatica is different between trees belonging to different layers, and how a possible difference can influence their successional dynamics. To accomplish these tasks, living and dead (both standing and lying) trees were mapped in four 0.56 ha plots. The relationship between trees, considering species, vegetative and social status, was analysed through univariate and bivariate point pattern analyses. Spatial structure based on tree size was investigated with Moran’s correlograms and a local indicator of spatial association. The spatial relationship between understory and canopy trees was also assessed using crown cover data to test for differences among the species. The upper layer is dominated by Q. petraea , whereas F. sylvatica was the only species in the suppressed one. The high amount of deadwood was mostly due to oak contribution. F. sylvatica living trees presented a clumped structure, while Q. petraea exhibited a random pattern. F. sylvatica dead trees showed instead repulsion to living ones. Suppressed trees were clumped at all distances, whereas trees belonging to dominant and intermediate strata were randomly distributed. Repulsion was found between the two species in the dominant layer. Beech recruitment occurred more frequently outside the canopy of dominant trees. Those beeches established under dominant tree showed a preference for oak cover. The succession from oak-dominated to beech-dominated stands has already reached an advanced stage in this old growth forest. The two species competitive interactions are mostly driven by their different shade tolerance and crown plasticity. Quercus – Fagus mixed stands like the Runcu-Grosi one should be preserved to maintain forest diversity and enhance forest resilience. Oak decline could be reduced by the occurrence of natural disturbances, together with active management that should be promoted to reduce beech competitive pressure.

Understanding how plants are constructed—i.e., how key size dimensions and the amount of mass invested in different tissues varies among individuals—is essential for modeling plant growth, carbon stocks, and energy fluxes in the terrestrial biosphere. Allocation patterns can differ through ontogeny, but also among coexisting species and among species adapted to different environments. While a variety of models dealing with biomass allocation exist, we lack a synthetic understanding of the underlying processes. This is partly due to the lack of suitable data sets for validating and parameterizing models. To that end, we present the Biomass And Allometry Database (BAAD) for woody plants. The BAAD contains 259 634 measurements collected in 176 different studies, from 21 084 individuals across 678 species. Most of these data come from existing publications. However, raw data were rarely made public at the time of publication. Thus, the BAAD contains data from different studies, transformed into standard units and variable names. The transformations were achieved using a common workflow for all raw data files. Other features that distinguish the BAAD are: (i) measurements were for individual plants rather than stand averages; (ii) individuals spanning a range of sizes were measured; (iii) plants from 0.01–100 m in height were included; and (iv) biomass was estimated directly, i.e., not indirectly via allometric equations (except in very large trees where biomass was estimated from detailed sub-sampling). We included both wild and artificially grown plants. The data set contains the following size metrics: total leaf area; area of stem cross-section including sapwood, heartwood, and bark; height of plant and crown base, crown area, and surface area; and the dry mass of leaf, stem, branches, sapwood, heartwood, bark, coarse roots, and fine root tissues. We also report other properties of individuals (age, leaf size, leaf mass per area, wood density, nitrogen content of leaves and wood), as well as information about the growing environment (location, light, experimental treatment, vegetation type) where available. It is our hope that making these data available will improve our ability to understand plant growth, ecosystem dynamics, and carbon cycling in the world's vegetation.

The horizontal and vertical distribution of live fine roots (diameter < 2 mm) of overstory Norway spruce [Picea abies (L.) Karst.] and their influence on diameter and height growth of underplanted beech (Fagus sylvatica L.) and Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) saplings were studied on experimental plots in the Solling Mountains (Germany). The aims of this study were to investigate how overstory fine root density varies with stand density, and how it influences growth of the underplanted saplings to changes in belowground resources availability in connection with simultaneously changing light availability. Most fine roots were concentrated in the humus layer (more than 45%) and in the top mineral soil (0-5 cm, about 15%). Fine root biomass increases with overstory basal area and decreases with rising distance from the nearest overstory tree, reaching about zero within ca. 8 m distance. Over the whole two-year study period, light availability alone was the decisive factor for growth of the beech saplings (5 resp. 6 years of age) while growth of the Douglas-fir saplings in the first study year (6 years of age) was additionally affected by a shortage of belowground resources due to root competition in a season with less than average rainfall. This species-specific response of underplanted saplings to changes in above and belowground resources is of silvicultural importance for the establishment of a mixed stand beneath a mature canopy: the more sensitive Douglasfir should be planted on the central parts of openings with little or none belowground competition while the less sensitive beech can be placed below the denser parts of the overstory. Se estudia la distribución horizontal y vertical de las raíces finas (diámetro < 2 mm) vivas del dosel de pinabete y su influencia en el diámetro y el crecimiento en altura de hayas plantadas y en brinzales de abeto Douglas en parcelas experimentales en las montes de Solling (Alemania). Los objetivos de este estudio es analizar cómo la densidad de raíces finas del dosel varía con la densidad del rodal, y cómo influye en el crecimiento de los árboles jóvenes del subpiso debido a los cambios en la disponibilidad de recursos en el suelo, en relación con el cambio al mismo tiempo en la disponibilidad de luz. Las raíces más finas se concentra en la capa de humus (más del 45%) y en la parte mineral superior del suelo (0-5 cm, aproximadamente el 15%). La biomasa de raíces finas aumenta con el área bisimétrica del dosel y disminuye con la distancia creciente al árbol más cercano del dosel, hasta llegar a cero dentro de ca. 8 m de distancia. Durante el periodo de estudio de dos años, la disponibilidad de luz era el único factor decisivo para el crecimiento de los plantones de haya (5 resp. 6 años de edad) mientras que el crecimiento de las plántulas de pino de Douglas en el primer año de estudio (6 años de edad) se vio afectado adicionalmente por la escasez de recursos en el suelo debido a la competencia de las raíces en una temporada con una precipitación menor del promedio. Esta respuesta especie-especifica de los árboles del subpiso a los cambios en los recursos por encima y por debajo del suelo es de importancia silvícola para la creación de una masa mixta bajo un dosel maduro: la especie más sensible, pino de Douglas, se debe plantar en las partes centrales de las aberturas con poca o ninguna competencia bajo tierra, mientras que el haya, menos sensible, se puede colocar debajo de las partes más densas del estrato superior.

International audience; Construction cost (g glucose g−1), chemical composition and morphology of leaves of beech (Fagus sylvatica L.) and two co-occurring valuable broadleaved species (sycamore maple - Acer pseudoplatanus L. - and ash - Fraxinus excelsior L.) were investigated along a horizontal light gradient (3-60% of above canopy radiation) and from top to bottom within the crowns in a fairly even-aged mixed-species thicket established by natural regeneration beneath a patchy shelterwood canopy.* Construction cost and carbon concentration increased with irradiance in ash and sycamore maple and were independent of irradiance in beech. Leaf traits expressed on an area basis, like construction cost, nitrogen content and leaf mass (LMA) increased significantly with irradiance in all three species and decreased from top to bottom within crowns.* The shade tolerant beech invested more glucose to produce a unit foliar biomass, but less to build a unit foliar area due to lower LMA. Thereby beech was able to display a greater total leaf area, what at least in parts counterbalanced the lower values of Na as compared to ash and sycamore maple.